(1) Field of the Invention
The invention relates to a circuit and a method for battery power receiving devices, and more particularly, to a continuous measurement of the charge and discharge of a battery in battery powered appliances as e.g. mobile phones to improve the accuracy of said measurement and the related charge control while introducing a solution with low power consumption.
(2) Description of the Prior Art
In a battery powered mobile unit or device it is necessary to monitor the battery charge status including monitoring the energy flow both into and out of the battery so that either parts of the functions of the device or the total device can be properly shut down before the battery supply voltage drops below a threshold for acceptable operation of the unit or proper actions are initiated to recharge the battery before said threshold is reached. Proper shutdown often involves saving configuration parameters in a non-volatile memory and/or providing either the user or an electrical or mechanical device with proper warning prior to shutdown.
One approach includes simply monitoring the battery voltage. A problem associated with this approach, however, is that the battery voltage, when measured at a point beyond the battery terminals, depends upon the ohmic losses or the drop in voltage caused by a current passing through a resistive path. In addition, the battery itself includes some variable ohmic loss, which is dependent upon the amount of charge remaining in the battery and the current being drawn from the battery. For example, a fully charged battery might measure 4.2 V at the terminals under a very small load such as  less than 1 mA, but measure 3.9 V under a load of 1 A. This voltage drop at the terminals is due to the output impedance of the battery. Thus, a half-discharged battery measuring 3.5 V at 1 mA might only provide 3.1 V under a 1A load. As example in a mobile phone having different modes as sleep, standby or transmit mode the load can vary significantly. A 3.4 V output voltage of a battery under xe2x80x9clightxe2x80x9d load conditions as standby or sleep requiring 10 mA may drop to 3.0 V under a 700 mA load.
In prior art the output voltage of a battery is often used to monitor the charge status of a battery. This is not well-suited to applications in which different modes of current loading are required. Because the voltage at the battery terminals can vary significantly among the various loads, selecting a single point under load at which e.g. to shut down would not be an efficient use of the battery, as certain applications would be closed prematurely.
U.S. Pat. No. 6,291,966 to Wendelrup et al. describes a battery system and method for supplying operating power during battery operation of a battery power receiving device. The battery system and method further includes a battery information circuit carried as a unit together with the battery means for assembly with the battery power receiving device. The battery information circuit includes memory cells and is capable of communicating information with the battery power receiving device.
U.S. Pat. No. 6,046,574 to Baranowski et al. discloses a mobile electronic device which can operate in multiple modes, each at a respective current load. Monitoring a battery in such a mobile device includes acquiring a sensed battery voltage during a particular operating mode and converting the sensed battery voltage to a scaled voltage for a known battery discharge curve having a well-defined turn-off voltage. The known battery discharge curve is preferably one for a full current load. The scaled voltage is then compared with the well-defined turn-off voltage to determine the amount of energy remaining in the battery.
U.S. Pat. No. 5,870,685 to Flynn shows a method and apparatus for controlling the operations of a battery-powered mobile station based on the capacity of its battery. The mobile station monitors the capacity of its battery to determine whether it has fallen below any one of a plurality of threshold capacity values. Different mobile stations operations are progressively disabled as the capacity of the battery falls below certain predetermined threshold levels. For a smart battery according to the Duracell/Intel specification a microprocessor can obtain the present capacity value directly from the smart battery. For a semi-smart battery, however, the battery may be initially conditioned, that is, completely discharged and then fully recharged from an external power source using, for example, a current shunt from the external power source to a current meter in the mobile station.
A principal object of the present invention is to provide a most accurate battery charge monitor continuously checking on the charge status of a battery of a battery driven appliance.
A further object of the present invention is to achieve a low current consumption of a said battery charge monitor.
In accordance with the objects of this invention, a circuit with the ability to monitor most accurately the charge/discharge status of a battery of a battery powered device is achieved. The circuit comprises, first, a battery to power said device, measuring means to measure the currents charging and discharging said battery, an external power supply, a reference voltage, mode setting means to set a specific mode of said mobile device, an input switching unit providing the input for the following components of the circuit and integrating means to integrate said currents charging/discharging the battery.
Furthermore the circuit comprises analog-to-digital converting means to enable digital processing within the monitor, compensating means to compensate the offset of said integrating means and up/down counting means representing the digital magnitude of the changes of the charge of said battery.
Furthermore the circuit comprises switching means having an input and an output wherein the input is the output of said up-and-down counting means and the output is fed to an accumulating means to accumulate said charge/discharge currents according to the sign of said up-and-down counting means, an accumulating means representing the absolute charge status of the battery and providing output to a controller unit managing the required actions related to said charge/discharge status of the battery and logic switching means controlling the timing of said input switching unit and of said integrating means integrating said currents charging/discharging said battery.
Furthermore in accordance with the objects of this invention, a circuit with the ability to monitor most accurately the charge/discharge status of a battery of a battery powered device is achieved.
The circuit comprises, first, a battery to power said device, measuring means to measure the currents charging and discharging said battery, an external power supply, a reference voltage, mode setting means to set a specific mode of said mobile device and switching means having an input and an output. Said input is a voltage representing said charge and discharge currents, said reference voltage, said indicator of a specific mode and a signal from a logic switching means controlling the timing of said input switching means and the output is switched to integrating means to integrate said charge/discharge currents over time to get the actual charge as an integral of currents.
Furthermore the circuit comprises said integrating means to integrate said charge/discharge currents having an input and an output wherein the input is a signal from a logic switching means controlling the timing of said means of integrating said charge/discharge currents and alternately, controlled by said logic switching means, said voltage representing said charge and discharge currents and, as output of additional compensating means to compensate the offset, a voltage representing the offset of said integrating means to integrate said charge/discharge currents or the input is shorted to convert the offset of said integrating means and the output is either the integral over time of the said measured charge/discharge currents or the converted offset during the time period while the input is shorted.
Furthermore the circuit comprises analog-to-digital converting means having an input and an output wherein the input is the output of said integrating means to integrate the charge/discharge currents and the output of said analog-to digital converting means is the digital magnitude of the integral of the charge/discharge currents or alternatively the digital magnitude of the offset of said integrating means to integrate the charge/discharge currents.
Furthermore the circuit comprises compensating means to compensate the offset of said integrating means, up/down counting means representing the digital magnitude of the changes of the charge of said battery having an input and an output. Said input is the output of said analog-to-digital converting means and said output of said up-and-down counting means is fed to a switching means which is forwarding said result of up-and-down counting to accumulating means to accumulate either a charge or a discharge accumulator according to the sign of the up-and-down counter.
Furthermore said switching means have an input and an output wherein the input is the output of said up-and-down counting means and the output is fed to said accumulating means to accumulate either a charge or a discharge accumulator according to the sign of the up-and-down counter.
Furthermore the circuit comprises an accumulating means representing the absolute charge status of the battery having an input and an output wherein the input is the output of said up/down counting means, a power supply voltage and the output is the input to a control unit representing the actual status of the charge and the discharge currents of said battery.
Finally the circuit comprises a logic switching means controlling the timing of said input switching unit and said integrating means to integrate said charge/discharge currents and of latching data in said accumulating means at the end of each time frame and a frame counting means defining time frames of a defined number of clock signals having an input and an output wherein the input is a clock signal and the output is an input of said logic switching means.
Also in accordance with the objects of this invention a method to monitor the charge status of a battery of a battery powered device is introduced. Said method comprises providing a battery to power said device, measuring means to measure the currents charging and discharging said battery, an external power supply, a reference voltage, an input switching unit, integrating means to integrate said charge/discharge currents, analog-to digital converting means, compensating means to compensate the offset of said integrating means and accumulating means to accumulate said digitized results of the integration of the currents representing the current status of the charge and discharge currents of said battery. The first step is to start with a defined charge status of said battery. The next step is to measure the charge/discharge currents followed by an integration of said charge/discharge currents while the offset of the integrator is compensated. Said digitized values representing the magnitude of the charge digitized are accumulated and finally the values of the charge/discharge currents according to the related accumulator values are signalled to a controlling unit.
Also in accordance with the objects of this invention a method to monitor the charge status of a battery of a battery powered device is introduced. Said method comprises providing a battery to power said device, measuring means to measure the currents charging and discharging said battery, an external power supply, a reference voltage, mode setting means to set a specific mode of said mobile device, an input switching unit, integrating means to integrate said charge/discharge currents, analog-to digital converting means, compensating means to compensate the offset of said integrating means, up/down counting means, means to forward said result of up/down counting to an accumulating means, an accumulating means representing the current status of the charge and discharge currents of said battery, and logic switching means controlling the timing of said input switching unit and said integrating means to integrate said charge/discharge currents and latching of data in said accumulating means at the end of each time frame and defining time frames of a defined number of clock signals. The first step is to start with a defined charge status of said battery. The mode of operation of the mobile device is defined influencing the dimension of power consumption and the resolution of the battery charge monitor. The charge/discharge currents are being measured. Said charge/discharge currents are being integrated while the offset of the integrator is being compensated the same time. The integrated values of previous step are converted from analog to digital values. The digitized values from the previous step are incremented according to sign of charge/discharge current in an up/down counter. The magnitude of the charge digitized in said up-down counter is added to either a charge accumulator or to the discharge accumulator. Overflows from the charge/discharge accumulators are used to clock additional registers and the signal values of the charge/discharge currents are signalled according to the related accumulator values to a controlling unit.